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Question from a non-physicist

  1. Mar 30, 2010 #1
    It is said that solid pieces of matter can never actually "touch", because the electrons in orbit around the nucleus of atoms will repel each other.

    my question is, what then accounts for friction?
  2. jcsd
  3. Mar 30, 2010 #2
    Sounds like I'm a "non-physicist" in this response, toooooo, but your "because the electrons in orbit around the nucleus of atoms will repel each other." sounds more like a philosophical question to me............. ummmmmmmmm, have you seen steel against steel? think they're "touching"........ ummmm, rubber against concrete.... think they're touching? if EVERY electron "repelled" every other electron, then the cell phone would slide off the desk, as would your coffee or soft drink............., so because these items DO IN FACT "touch', slike them, and there's friction.

    Now if I had a super electro microscope, I could see WHAT was touching WHAT to make that friction, but, well, I'm going in circles.

    Ever hold your finger against a spinning wood piece on a lather? or hold your finger tight on a bicycle wheel tire while somebody cranks it? You are TOUCHING it, your muscles HOLDS it there, and hoping that the electrons will REPEL you will STILL get you burned.

    Yes, I agree, we need a REAL scientist to answer this one.

    LarryR : )
  4. Mar 30, 2010 #3
    Friction is also due to those electromagnetic forces because they do not let macroscopic objects pass trough one another. At a macroscopic scale the surfaces of materials look smooth but when you zoom in those surfaces are very rough. Something like ___/^|_____/^|____/^|_/\__/^\__ . If you put two such surfaces together the imperfections in the surface (asperities) will touch one another.When you try to move the two surfaces all the imperfections on a surface apply a force on the imperfections on the other surface and by the third law the other will apply a equal opposite force on them.The coefficient of friction of a material is mostly determined by the imperfections on the surface.You must realize that the asperities are extremely large in comparison with atoms. So you can think of the forces between the imperfections in a very 'Newtonian mechanics way' but the origin of the forces is ultimately electromagnetic(the repulsion of charges).
    Here you can find a lot about friction.
  5. Mar 31, 2010 #4

    Andy Resnick

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    We do not yet have a rigorous theory of friction- we have only phenomenological theories. Friction is currently modeled as a dissipative process that generates heat; that's really as far as we can currently go.
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